Electric motor fuel pumps have been widely used to supply the fuel demand for an operating engine, such as in automotive applications. These pumps may be mounted directly within a fuel supply tank and have an inlet for drawing liquid fuel from the surrounding tank and an outlet for delivering fuel under pressure to the engine. The electric motor includes a rotor mounted for rotation within a stator in a housing and connected to a source of electrical power for driving the rotor about its axis of rotation. In so-called turbine or regenerative type fuel pumps, an impeller is coupled to the rotor for co-rotation with the rotor and has a circumferential array of vanes about the periphery of the impeller. One example of a turbine fuel pump of this type is illustrated in U.S. Pat. No. 5,257,916.
A typical turbine-type fuel pump has an impeller with opposed generally planar faces disposed between two plates each having a generally planar face adjacent to the impeller. The clearance between the adjacent faces of the impeller and plates is usually made small to, among other things, reduce leakage. However, reducing the clearance between the plates and the impeller can unduly increase the friction between them and thereby affect the performance of the fuel pump. Accordingly, the impeller and the adjacent faces of the plate are manufactured to close tolerances to provide a desired clearance between them.